1. Field of the Invention
The present invention relates to an apparatus and method for controlling a driving motor, and specifically relates to an apparatus and method for controlling a driving motor which drives a driven device by a gear system.
2. Description of the Related Art
FIG. 1 briefly shows the construction of a typical driving device for driving a driven device. FIG. 2 is a section view of the device of FIG. 1 viewed from line VIII--VIII.
Driving gear 55, which is a flat gear, is connected to the tip of drive shaft 53 of driving motor 51 controlled by controller 57. On the other hand, driven gear 63, which is a flat gear, is connected to the tip of driven shaft 61 of driven device 59. Driving gear 55 and driven gear 63 are mutually engaged, such that the drive force of driving motor 51 is transmitted to driven device 59. As shown in FIG. 2, cog 65a of driving gear 55 makes contact with cog 67a of driven gear 63, but cog 65b and cog 67a do not make contact via a backlash. The backlash is the clearance between cog surfaces and is provided to allow smooth rotation of the gears.
FIG. 3 shows the types of patterns of stopping controls executed by controller 57 of driving motor 51 shown in FIG. 1.
FIG. 3(A) shows a control pattern when the speed of a driving motor is stopped directly from a stationary speed in time t at which a stop command for a driven device is output.
FIG. 3(B) shows a control pattern when the speed of a driving motor is linearly slowed down from a stationary speed in time t.
FIG. 3(C) shows a control pattern when the speed of a driving motor naturally slows down in conjunction with the rotational inertias of the driving gear and the driven gear in time t with the driving motor current switched OFF.
Various disadvantages arise in the aforesaid stopping controls of a driving motor.
In the control shown in FIG. 3(A), loud impact noise is produced during stopping because the driven device is stopped in a short time. FIG. 4 illustrates impact reduction in such an instance, and corresponds to the gear linkage state shown in FIG. 2.
From the state shown in FIG. 2, the driving motor speed becomes zero [0] at time t according to the control pattern of FIG. 3(A) to abruptly stop driving gear 55. Since a backlash is provided for both gears and driven gear 63 which is driven up to that time is not directly stopped by rotational inertia, cog 67a of driven gear 63 continues to rotate in a counterclockwise direction until contact is made with cog 65b of stopped driving gear 55, as shown in FIG. 4. Thus, a loud noise is produced by the impact of cogs 67a and 65b. Impacted cog 67a is reversely rotated in a clockwise direction by the reaction of the impact with cog 65b so as to again abut cog 65a, and the rotational vibration of gear 63 is repeated so as to again contact cog 65a, thereby readily producing a noise source. Although the aforesaid disadvantage can be avoided if the clearance of the cogs, i.e., backlash, is eliminated, a backlash is a mechanical necessity for gear systems.
On the other hand, comparison of the control which linearly slows down the speed of the motor such as shown in FIG. 3(B) and the natural stopping control through rotational inertia such as shown in FIG. 3(C) shows that gear 55 is not stopped abruptly. Although these stopping methods are advantageous in reducing noise generated by the impact of driven gear 63, they are disadvantageous in that a long time is required to completely stop the driven device.
When control is implemented to accelerate the stopping control to produce an abrupt drop in the speed of the driving motor as shown in FIG. 5 so as to stop a driven device within the time restriction allowed to stop the driven device, a disadvantage similar to that produced by the control pattern of FIG. 3(A) occurs, i.e., loud noise is generated. In recent years, the problem of noise in office automation equipment has not been adequately addressed relative to driving control of a driven device in the complex repetition of stopping controls.
An object of the present invention is to eliminate the previously described disadvantages by providing a control device for a driving motor capable of reducing as much as possible the noise generated by the impact of gears, and slowing down the speed or stopping a driven device in a short time when reducing the speed or stopping a driven device.